Pre-equilibrium particle emission from fusion of /sup 12/C + /sup 158/Gd and /sup 20/Ne + /sup 150/Nd

Journal Article · Tue Aug 01 00:00:00 EDT 1978 · Phys. Rev., C; (United States)

DOI:https://doi.org/10.1103/PhysRevC.18.796· OSTI ID:6678653

Westerberg, L; Sarantites, D G; Hensley, D C; Dayras, R A; Halbert, M L; Barker, J H

Neutron time-of-flight spectra and ..cap alpha..-particle spectra were obtained in coincidence with ..gamma.. rays characteristic of specific evaporation residues in the reactions 174.8 MeV /sup 20/Ne + /sup 150/Nd and 152.0 MeV /sup 12/C + /sup 158/Gd, producing /sup 170/Yb at 134.2 and 132.0 MeV of excitation. The average multiplicity of ..gamma.. rays associated with such coincident events were also determined. The neutron spectra from the /sup 20/Ne reactions are characteristic of equilibrium evaporation processes. They show a temperature t approx. 2 MeV, in agreement with a prediction from level-density parameters based on data at far lower excitation energy. The neutron spectra from the /sup 12/C reactions show a low-temperature equilibrium component (average t approx. 1.8 MeV) and a high-temperature (t approx. 6 MeV) pre-equilibrium component. The latter observation may be interpreted as evidence for the transient existence of a hot spot involving no more than 25 nucleons. The estimated number of pre-equilibrium neutrons emitted varies from 1.8 to 0.6 for the 8n to 10n products and from 1.2 to 0.25 for the ..cap alpha..6n to ..cap alpha..9n products. The fraction of /sup 166-x/Er products formed by 2p (x + 2) n rather than ..cap alpha..xn emission decreases with increasing x for both thee /sup 20/Ne and /sup 12/C reactions, and is roughly twice as large for /sup 12/C. The high-energy portions of the ..cap alpha..-particle spectra from (/sup 12/C,..cap alpha..xn) for small x exhibit a strong dependence on exit channel and on angle of emission, indicating clearly that these ..cap alpha.. particles are emitted from a nonequilibrated system. The angular correlations of the higher-energy ..cap alpha.. particles from (/sup 12/C,..cap alpha..7n) to (/sup 12/C,..cap alpha..10n) all have the same shape, suggesting that in these channels the ..cap alpha.. emission occurs first. The pre-equilibrium emission accounts for (16 +- 7) % and (28 +- 6) % of the total (/sup 12/C,xn) and (/sup 12/C,..cap alpha..xn) cross sections, respectively.

• Research Organization: Department of Chemistry, Washington University, St. Louis, Missouri 63130
• OSTI ID: 6678653
• Journal Information: Phys. Rev., C; (United States), Journal Name: Phys. Rev., C; (United States) Vol. 18:2; ISSN PRVCA
• Country of Publication: United States
• Language: English

Related Subjects

651825* -- Nuclear Properties & Reactions
A=150-189
Experimental-- Nuclear Reactions & Scattering-- (-1987)
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ALPHA SPECTRA
CARBON 12 REACTIONS
CHARGED-PARTICLE REACTIONS
COINCIDENCE SPECTROMETRY
CROSS SECTIONS
ENERGY RANGE
EVAPORATION MODEL
EVEN-EVEN NUCLEI
EXCITATION FUNCTIONS
FUSION REACTIONS
GADOLINIUM 158 TARGET
GAMMA SPECTRA
HEAVY ION REACTIONS
INTERMEDIATE MASS NUCLEI
ISOTOPES
MATHEMATICAL MODELS
MEV RANGE
MEV RANGE 100-1000
MULTIPLICITY
NEODYMIUM 150 TARGET
NEON 20 REACTIONS
NEUTRON SPECTRA
NUCLEAR MODELS
NUCLEAR REACTIONS
NUCLEI
PRECOMPOUND-NUCLEUS EMISSION
RARE EARTH ISOTOPES
RARE EARTH NUCLEI
SPECTRA
STABLE ISOTOPES
TARGETS
TIME-OF-FLIGHT METHOD
YTTERBIUM 170
YTTERBIUM ISOTOPES